<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Monitor</title>
    <script src="../../vue.js"></script>
</head>
<body>
    <div id="app">
        <input type="text" v-model="cityName">
        <p>{{message | toUpcase}}</p>
        <div v-bind:id="dataId | formatId">helloworld</div> 
    </div>
    
    <script>
        var vm=new Vue({
            el:'#app',
            data:{
                cityName:'shanghai',
                message:'helloworld',
                dataId:'dff1',
            },
            watch:{
                cityName(newName,oldName){
                    console.log(newName,oldName)
                }
            },
            filters:{
                toUpcase(value){
                    return value ? value.toUpperCase():''
                },

                formatId(value){
                    return value ? value.charAt(1)+value.indexOf('d'):''
                }

            }

        })
    </script>
</body>
</html>